1. Field of the Invention
The present invention relates to a flux for soldering and a solder paste composition.
2. Description of the Related Art
A solder paste composition used in mounting an electronic component on a board is prepared by mixing a flux for soldering and a solder alloy powder. When soldering is done with the use of this solder paste composition, a part of the flux for soldering tends to remain in the vicinity of a solder-jointed part on a board as a flux residue.
In general, the above mentioned flux for soldering contains a base resin, an activating agent and a solvent. In addition, as this base resin, a rosin is widely used conventionally.
In accordance with the recent higher performance, densification or the like of an electronics product, situations are increasing where a board is exposed to an environment having drastic changes in temperature. Under such an environment, a flux residue that is formed by using a flux for soldering, in which a rosin is used as a base resin, is easy to become hard and fragile, due to its inherent nature. Furthermore, the above mentioned flux residue becomes easy to crack with time. Accordingly, through the crack, water becomes easy to infiltrate a circuit part of a board, thereby creating problems including the short-circuit of a circuit and the metal corrosion of the circuit.
As a method for solving the above mentioned problems, there is a method for preventing the flux residue from remaining on a board at the completion of soldering, without incorporating any rosin into a flux for soldering, as disclosed in, for example, JP 2006-289497 A. In addition, there is a method in which another resin instead of a rosin is used as a base resin, or a rosin and another resin are used together, as disclosed in, for example, JP 2011-121059.
However, even when such a flux for soldering disclosed in JP 2006-289497 A mentioned above is used, it is difficult to completely eliminate the flux residue. In addition, a solder paste composition, in which a flux for soldering with the rosin content reduced is used, reduces the reflow property. Accordingly, it is necessary to increase the content of an activating agent for such a solder paste composition, which may disturb the printability of the solder paste composition.
In addition, a flux for a solder paste disclosed in JP 2011-121059 A mentioned above needs to incorporate a given amount of rosins, for the purpose of improving the printability of a solder paste composition. Accordingly, the flux residue that is formed by using such a solder paste composition causes uncertainty involving the crack initiation or development under an environment having drastic changes in temperature.